Is this a well known feature or something I've managed to bring on
myself through an excess of customization?

Try this:  In the windows search tool specify
All or part of file name: .java
A word or phrase in the file: import
Look in: <some directory with java files>

I've tried this on three different work stations and the result has
always been:

"Search Complete: No results to display"

Same thing happens searching for common statements inside .jsp and .bas
files.

PS: I also have "search system files" enabled, so they are not being
skipped for that reason